This invention concerns an angle type power nutrunner having a housing with a rotation motor, an angle head with an output shaft, and a thread connection for securing the angle head to the housing and including mating threads on the angle head and the housing and a lock nut.
Power nutrunners of this type are previously well known and may be exemplified by U.S. Pat. No. 4,064,948. The angle nutrunner disclosed in this patent lacks however a lock nut, which means that there is no provision made for angular adjustability of the angle head in relation to the tool housing. In later modifications of this nutrunner, the thread connection between the angle head and the housing does comprise a lock nut to enable setting and securing of the angle head in desired angular positions. Such an adjustability of the angle head is important for the operator to obtain a comfortable working posture.
This prior art nutrunner has a drawback in that it is difficult to have its angle head secured in a desired angular position during assembly of the tool. In other words, it is difficult to maintain the angle head in a correct desired angular position when tightening the lock nut.
Another drawback of this known angle nutrunner is that the lock nut arrangement for rotational locking of the angle head to the housing relies on friction forces only. This has been considered unsatisfactory from the safety point of view, because the frictional locking accomplished by the lock nut may not always withstand the reaction torque transferred between the angle head and the housing. This could result in an undesireable movement between the angle head and the housing during operation of the tool, which would be hazardeous to the operator.
In another prior art angle nutrunner, disclosed in U.S. Pat. No. 4,458,565, the angle head is axially clamped to the tool housing by means of a threaded sleeve, whereas axially directed teeth on the angle head engage a lock pin on the tool housing to positively lock the angle head against rotation.
Alternative angular positions of the angle head are obtained by loosening the threaded sleeve and moving the angle head into a new position where another one of the teeth engages the lock pin, and then retightening the sleeve.
Still another interesting piece of prior art refers to certain types of pneumatic chisel hammers wherein a thread connection between the cylinder of the impact mechanism and the tool handle comprises a lock pin which engages simultaneously one hole of a circumferential row of holes in the handle and one hole of a circumferential row of holes in the cylinder, wherein the pitch of the holes in the handle is different from the pitch of the holes in the cylinder.
Although, this previously known locking means has a certain resemblance with the present invention, it is important to notice that this known device is a pure thread locking device intended to be engaged after the thread connection has been firmly tightened and to maintain the thread connection in that firmly tightened state. This is very much the same thing as a cotter pin locking of a slotted nut and is not intended to define any other angular positions between the threaded parts than the fully tightened position.